Deepwater Pipelaying Operations And Techniques Utilizing J-Lay Methods

Abstract

ABSTRACT As part of the planned offshore installation of the 12" Oil and 12" Gas pipelines connecting the Auger Tension Leg Platform (TLP) to two (2) shallow water platforms located in the Vermilion and Eugene Island Areas, Offshore Louisiana, Shell Oil Company required the use of J-Lay pipelaying techniques for the installation of the Phase 11 deepwater portions of the Auger pipelines ranging from water depths of 7200 feet to 2860 feet. This paper describes the J-Lay Pipelay System utilized to install the deepwater portions of the Auger 72" pipelines and the means by which pre-fabricated pipe joints were assembled, handled, and installed utilizing J-Lay methods and techniques. As evidenced by the successful installation of the Auger pipelines, this new technology provides proven, reliable methods in which deepwater pipelaying operations can be performed beyond the limits of conventionally moored SLay or Reel-Lay pipelaying vessels. INTRODUCTION In 1990 and 1991, McDermott Marine Construction was awarded two (2) contracts to install a total of 108 miles of 12" pipelines in two (2) phases, Phase I consisted of the installation of a 52-mile segment of 12" Oil pipeline originating in a water depth of 243 feet and a 16-mile segment of 12" Gas pipeline originating in a water depth of 396 feet. Pipelay operations were conducted utilizing a conventionally moored S-Lay pipelaying barge. The Phase I S-Lay pipeline segments converged at a seafloor termination point in the Garden Banks Area and were abandoned approximately 600' apart on the seafloor with specially designed diverless abandonment and recovery heads in 1200 feet of water. Phase II J-Lay operations consisted of recovering the ends of the 12" Oil and 12" Gas pipelines in 1200 feet of water and installing approximately 40 miles (two segments at 20 miles each) of 12¾" × .562" X-52 pipeline to the Auger TLP located in 2860 feet of water. The Phase II J-Lay contract was awarded in October, 1990. Design, fabrication and pre-mobilization assembly and testing of the J-Lay System spanned a period of thirty (30) months. The J-Lay System was mobilized to the field in April, 1993 ready to commence J-Lay operations. J-LAY SYSTEM REQUIREMENTS During pre-contract award meetings and discussions with Shell Oil Company, as well as throughout the actual design and fabrication stages of the development of the J-Lay System, several requirements were identified by a project planning team consisting of design and project engineering personnel, as well as key offshore operations personnel assigned to operate the system during actual offshore construction. The following summarizes the major requirements that formed the basis for the development of the present J-Lay System. DP Vessel Compatibility Achieving and maintaining the station keeping ability of the pipelay barge or vessel is essential to conducting pipelay operations within the limits of the allowable pipeline bending strains. Although opinions vary regarding the water depth limits to which conventionally-moored pipelay barges or vessels can maintain station keeping ability, project requirements dictated that the J-Lay System developed for the Auger pipeline project be designed for operation on a dynamically positioned (DP) vessel.